1. Field of the Invention
The present invention relates to a magnetic video reproducing apparatus. More particularly, it relates to a magnetic video reproducing apparatus which is so improved as to maintain excellent quality of reproduced pictures when reproduction is made at a speed several times faster than the recording speed.
2. Description of the Prior Art
In a conventional home magnetic video reproducing apparatus and a magnetic video recording/reproducing apparatus having a picture recording function, there are generally employed a rotating head system, a helical scanning system and an azimuth system. In the rotating head system, e.g., two video heads are mounted on the circumference of a rotating drum to be separated from each other at an angle of 180.degree. . In the helical scanning system, a magnetic tape is made to travel aslant with respect to the video heads. In the azimuth system, gaps of the two video heads are provided at angles different from each other, so that angles of video signals recorded in the magnetic tape vary with the video heads.
These three systems are disclosed in detail in, e.g., U.S. Pat. No. 4,463,390 issued on July 31, 1984 to Yoshio Koga et al.
The present invention is directed to an improvement in a magnetic video reproducing apparatus employing the above three systems.
FIG. 1 is illustrative of a video recording/reproducing portion of a conventional magnetic video reproducing apparatus and a magnetic tape in which video signals are recorded by the conventional video recording portion. Referring to FIG. 1, a video recording portion 10 includes a head drum 11 rotatably provided at a position in the travelling path of the magnetic tape. The head drum 11 is provided on its circumference with two video heads 12 and 13 which are separated at an angle of 180.degree. from each other for recording and/or reproducing video signals. Slantingly guided along the head drum 11 is a magnetic tape 1 which is wound around a supply reel 14 and a take-up reel 15, to implement the helical scanning system in which the magnetic tape 1 travels aslant with respect to the direction of rotation of the video heads 12 and 13, i.e., the direction of rotation of the head drum 11. In the vicinity of the take-up reel 15, there are provided a capstan 16 and a pinch roller 17 with interposition of the magnetic tape 1 therebetween.
Thus, in the magnetic video reproducing apparatus employing the helical scanning system, magnetic patterns of the video signals to be recorded in the magnetic tape 1 are as shown in FIG. 1. Further, when the video signals are recorded by, e.g., the VHS system, recording is made with a recorded A track 2 and a B track 3 in process of recording at azimuth angles of, e.g., 6.degree. and -6.degree. respectively. In FIG. 1, symbol X indicates the direction of travelling of the magnetic tape 1 and symbol Y indicates the direction of rotation of the video heads 12 and 13.
FIG. 2 is a circuit diagram of a conventional magnetic video reproducing apparatus. In structure, the conventional magnetic video reproducing apparatus includes a head drum 11 having video heads 12 and 13, a rotary transformer assembly 23 coupled with the head drum 11, a recording system block 21, a reproducing system block 24, a head changeover switch assembly 22 for performing switching operation between the recording system block 21 and the reproducing system block 24 with respect to the rotary transformer assembly 23, a tape travel driving circuit 25 and a mode selection switch assembly 26. The recording system block 21 includes a video signal source 211 for generating video signals, a luminance signal pass filter 212 for separating luminance signals from the video signals, a color signal pass filter 213 for separating color signals from the video signals, an FM modulator 214 for performing FM modulation of the luminance signals, a low frequency converter 215 for performing low frequency conversion of the color signals and an adder 216 for adding up modulated or converted luminance signals and color signals. The reproducing system block 24 includes head amplifiers 241 and 242 for amplifying signals detected by the respective video heads 12 and 13, an adder 243 for adding up the outputs from the head amplifiers 241 and 242, an FM video signal pass filter 244 for separating luminance signals from the added signals, an FM demodulator 245 for performing FM demodulation, a low frequency color signal pass filter 246 for separating color signals from the added signals, a high frequency converter 247 for performing high frequency conversion, an adder 248 and an output terminal 249. The mode selection switch assembly 26 is coupled to the tape travel driving circuit 25, and includes a recording command switch 261, a reproduction command switch 262, a stoppage command switch 263, a fast reproduction command switch 264 and a temporary stoppage command switch 265. Each of these switches 261 to 265 is adapted to supply the tape travel driving circuit 25 with the subject command when the same is turned on. The tape travel driving circuit 25 drives and controls the head drum 11, the supply reel 14, the take-up reel 15, the capstan 16 and the head changeover switch assembly 22 based on outputs from the aforementioned mode selection switch assembly 26.
Referring to FIGS. 1 and 2, operation of the conventional magnetic video reproducing apparatus is now described.
First, explanation is made with respect to signal processing in a recording mode. When the recording command switch 261 of the mode selection switch assembly 26 is turned on, the magnetic video reproducing apparatus is brought in the recording mode, in which switches 221 and 222 respectively included in the head changeover switch assembly 22 are switched upwardly, i.e., toward contacts A in FIG. 2 by the tape travel driving circuit 25, so that the head drum 11 and the capstan 16 etc. are driven at a predetermined recording speed. A video signal generated from the video signal source 211 consist of a luminance signal of up to about 3 MHz and a color signal of 3.58 MHz. The luminance signal includes horizontal synchronizing signals and vertical synchronizing signals, and the color signal includes color-burst signals. The luminance signal passes through the luminance signal pass filter 212 to be supplied to the FM modulator 214. The FM modulator 214 modulates the luminance signal to an FM signal of 3.4 MHz to 4.4 MHz, which is supplied to the adder 216. On the other hand, the color signal passes through the color signal pass filter 213 to be supplied to the low frequency converter 215. The low frequency converter 215 converts the color signal into signal of 629 KHz, to supply the same to the adder 216. The adder 216 adds up the FM-modulated luminance signal and the low-frequency converted color signal. The added signal, i.e., the frequency-modulated video signal is supplied to the video head 12 through the switch 221 included in the head changeover switch assembly 22 and a transformer 231 included in the rotary transformer assembly 23, as well as to the video head 13 through the switch 222 and a transformer 232 included in the rotary transformer assembly 23. The video head 12 records the modulated video signal, i.e., the luminance signal and the color signal on the A track 2, while the video head 13 records the modulated video signal on the B track 3.
Explanation is now made on signal processing in a reproducing mode. In a normal reproducing mode, the reproduction command switch 262 in the mode selection switch assembly 26 is pushed down to be on. In response, the tape travel driving circuit 25 switches the respective switches 221 and 222 included in the head changeover switch assembly 22 downwardly in FIG. 2, i.e., toward contacts B to switch to the reproducing mode and drives the head drum 11 and the capstan 16 etc. in a similar manner to the recording mode.
The recorded signal, i.e., the video signal recorded on the A track 2 of the magnetic tape 1 is selected by the azimuth angle to be read by the video head 12, and is supplied to the head amplifier 241 through the transformer 231 and the switch 221. The head amplifier 241 amplifies the reproduced signal to supply the same to the adder 243. Similarly, the recorded signal recorded on the B track 3 of the magnetic tape 1 is read by the video head 13, to be supplied to the head amplifier 242 through the transformer 232 and the switch 222. The head amplifier 242 amplifies the reproduced signal to supply the same to the adder 243.
The adder 243 adds up the reproduced signals on the A track 2 and the B track 3, to supply the same to the FM luminance signal pass filter 244 and the low frequency color signal pass filter 246. The FM luminance signal pass filter 244 passes the FM luminance signal within the frequency range modulated by the FM modulator 214 alone, to supply the same to the FM demodulator 245. The FM demodulator 245 demodulates the FM luminance signal to extract luminance signal, which is supplied to the adder 248. On the other hand, the low frequency color signal pass filter 246 passes the low frequency color signal within the frequency range converted by the low frequency converter 216 alone, to supply the same to the high frequency converter 247. The high frequency converter 247 converts the low frequency color signal into the color signal of 3.58 MHz, to supply the same to the adder 248. The adder 248 adds up the demodulated luminance signal and the color signal, to output a reproduced composite video signal to the output terminal 249.
Fast reproducing operation is now explained. In the fast reproducing operation, the capstan 16 is rotated by the tape travel driving circuit 25 at a speed in a predetermined multiple of the recording speed, e.g., by four times according to operation of the fast reproduction command switch 264. Consequently, the magnetic tape 1 travels at a speed, e.g., four times faster than the tape travelling speed in the recording operation, and the video heads 12 and 13 cannot trace certain tracks, to successively miss the tracks. When, it is assumed that the A tracks and the B tracks are alternately arranged, for example, and the video head 12 misses a B track for shifting from an A track to the following A track and the video head 13 misses an A track for shifting from a B track to the following B track, the outputs of the video heads 12 and 13 are lowered, followed by lowering of the outputs of the adder 243 which adds up the outputs from the head amplifiers 241 and 242, whereby noises appear in the reproduced composite video signals and on the screen 100 of a monitor television.
Further detailed explanation is made with reference to FIG. 3. FIG. 3 illustrates relation between the video signal before demodulation, i.e., the output from the adder 243 (see FIG. 2), the reproduced composite video signal, i.e., the output from the adder 248 and the noises appearing on the monitor screen 100. The ordinate in FIG. 3 represents passage of time, which passes downwardly from the upper part. As described above, when, for example, the video head 12 misses the B track for shifting from an A track to the following A track and the video head 13 misses the A track for shifting from a B track to the following B track, the outputs thereof are lowered such that noises 103 appear in the outputs of the adder 243. Thus, the noises 103 also appear in the reproduced composite video signal, i.e., the output from the adder 248 generated by demodulation of the subject output of the adder 243. In the output from the adder 248 as shown in FIG. 3, the video signal portion is indicated by the reference numeral 104 and the synchronizing signal portion is indicated by the reference numeral 105. Since the reproduced composite video signal outputted from the adder 248 is displayed on the monitor screen 100, the noises 103 appear on the same as, e.g., three screen noises 200 in the upper, middle and lower portions of the screen 100. Thus, the picture displayed on the monitor screen 100 are blurred when the same are reproduced at a high speed.